Which defects can be fixed from the pit during a F1 race?

What technical defects can be fixed from the paddock during a race?

In practise nothing. If telemetry signals that a sensor is broken, then the pit can communicate to the driver what changes to make. This way you can bypass a single broken sensor, which could affect the performance of the car. Direct manipulation of the car's settings is not allowed from the pits. Telemetry data is read only.